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Questions and Answers
What role do guard cells play in the functioning of stomata?
What role do guard cells play in the functioning of stomata?
Which mechanism primarily drives water movement through the xylem?
Which mechanism primarily drives water movement through the xylem?
What is the apoplast pathway in water movement?
What is the apoplast pathway in water movement?
What occurs when xylem vessels break, according to the cohesion-tension theory?
What occurs when xylem vessels break, according to the cohesion-tension theory?
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How does water exit xylem vessels to enter leaf cells?
How does water exit xylem vessels to enter leaf cells?
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What is the primary driving force behind transpiration?
What is the primary driving force behind transpiration?
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Which statement correctly explains cohesion in water movement?
Which statement correctly explains cohesion in water movement?
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What role does root pressure play in water movement?
What role does root pressure play in water movement?
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Study Notes
Water Movement in Plants
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Water enters root hair cells through osmosis, moving through the root cortex and into the xylem, then ascending to leaves.
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Transpiration is the evaporation of water from mesophyll cells in leaves, exiting through stomata.
Mechanisms of Xylem Water Movement
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Cohesion: Hydrogen bonds between water molecules create a continuous column.
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Cohesion-tension theory: Water is pulled upwards due to the tension created by transpiration, forming a continuous water column.
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Adhesion: Water adheres to xylem walls, further aiding upward movement.
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Capillarity: The combined effects of cohesion and adhesion allow water to rise in narrow xylem vessels.
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Root pressure: Osmotic pressure in roots contributes to upward water movement.
Cohesion-Tension Theory
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Mechanism: Transpiration at leaves creates tension, pulling water up from the roots. Low water pressure in the xylem maintains the water column.
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Evidence: Trunk diameter changes correlate with transpiration rates. Air drawn into broken xylem vessels supports the tension-based water movement concept.
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Criticisms: Although a broken water column should halt flow, water can bypass blockages through xylem pits.
Water Movement from Xylem to Leaf Cells
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Water moves via pits from xylem vessels into leaf cells. This movement follows the water potential gradient.
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Pathways: Two main pathways exist:
- Apoplast: Movement through cell walls and intercellular spaces.
- Symplast: Movement through cytoplasm, connected via plasmodesmata.
Transpiration Process
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Water evaporates from mesophyll cells, saturating leaf air spaces.
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A water vapor gradient between the leaf and atmosphere drives water loss through stomata.
Function and Mechanism of Stomata
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Role: Stomata regulate gas exchange, crucial for photosynthesis.
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Opening Mechanism:
- Guard cells actively expel hydrogen ions.
- This triggers potassium ion channels to open, allowing potassium ions to enter the guard cells.
- Increasing potassium concentration lowers the water potential in guard cells, drawing in water.
- Increased turgor pressure in guard cells opens stomatal pores.
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Description
Explore the fascinating mechanisms of how water moves through plants, focusing on osmosis, transpiration, and the cohesion-tension theory. This quiz will test your understanding of xylem function and the physiological processes involved in water transport.
